Method and apparatus for a mobile station to enhance the probability of successful emergency call completion and successful callback from emergency service centre

ABSTRACT

A method and apparatus for enhancing the probability of a successful emergency call completion and emergency callback on a mobile station in a network, the method comprising the steps of: during an emergency call attempt, monitoring whether the mobile station has received a non-voice service request from the network and, if yes, ignoring the non-voice service request. Further, during a callback period, monitoring whether the mobile station has received a service request from the network and, if yes, ignoring the service request if the service request is a non-voice service request that is anything but a position location service request. Further, during a callback period, monitoring whether a user attempts to initiate a non-voice service request that is anything but a position location service request, and if yes ignoring the non-voice service request.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority from U.S. provisionalapplication Ser. No. 60/441,504 filed on Jan. 21, 2003, the completedrawings and specification of which are incorporated herein byreference.

FIELD OF THE INVENTION

This application relates to mobile communication techniques in general,and to a method and apparatus for a mobile station to enhance theprobability of successful emergency call completion and successfulcallback from emergency service centre in particular.

BACKGROUND TO THE INVENTION

A regulatory body having a jurisdiction over classes of mobilecommunication systems imposes the requirement of an emergency service.For instance the Federal Communications Commission's (FCC's) ordersdocket 94-102 for Wireless E911 service, an exemplary emergency service,both in spirit and by order, intends that wireless subscribers, with ahigh probability of success, can:

-   -   Perform timely call completions for emergency calls;    -   Initiate emergency calls on any available wireless system;    -   Receive emergency callback service for a specific time duration,        once the emergency call serving network is aware of the        subscribers callback number; and    -   Be provided with clear notification of outgoing emergency calls.

Although regulatory bodies differ in jurisdiction and class of mobilecommunication systems, all communication systems would benefit from theenhanced probability of successfully completing a call to emergencyservices.

SUMMARY OF THE INVENTION

The details of a method and apparatus for a mobile station to enhancethe probability of successful emergency call completion and successfulcallback from emergency service centre disclosed herein enable mobilestations (MSs) to enhance the probability of successful emergency callcompletion and successful callback from an emergency service centre.

A particular area of emergency services that is an object of the presentapplication is the handling of network-initiated events that mayotherwise interfere with emergency call handling and/or emergencycallback service. Examples are network-initiated short message service(SMS) or push packet data service. Special handling of these casessignificantly increases the probability of success for emergencyservices.

A typical implementation of emergency call handling is such that theMobile Station (MS) may be allowed to acquire or camp on any systemregardless of whether the system is preferred or not—even if SIM(Subscriber Identity Module) or RUIM (Removable User Identity Module) isnot present. After the emergency call ends, the MS may stay on the lastserving system for certain duration, which is known as the callbackperiod. In one embodiment the MS may stay on the last serving system forapproximately 5 minutes. One skilled in the art will realize that otherdurations are possible or may be more desirable. The user may bevisually notified of the callback mode. The purpose of the callback modeis to ensure that the MS stays on the last system so that emergencyservice centre (e.g. Public Safety Answering Point or PSAP) can callback the user.

During the emergency call origination attempts, the MS may receiverequests from the network to set-up other services. If the MS acceptssuch requests, the emergency call attempts may get terminated. If thewireless network receives the emergency call attempt, then the onlyrequirement for the network may be to grant it highest priority in itsqueue so that it can be serviced with utmost priority. However, thenetwork may not keep any information about the MS after the emergencycall ends. As a result, it may initiate a non-urgent non-voice serviceduring the callback period. If that happens and the MS accepts theservice, the emergency call centre may not be able to call the MS duringsuch sessions

It is an object of the present application that a method and apparatusfor a mobile station to enhance the probability of successful emergencycall completion and successful callback from emergency service centre isprovided at a MS to enable the MS to make intelligent decisions as towhen it can reject non-emergency-voice services, as well as to when toaccept all services without dropping emergency voice services.

The present invention therefore provides a method of enhancing theprobability of a successful emergency call completion on a mobilestation in a network, comprising the steps of: during an emergency callattempt by a mobile station, monitoring whether the mobile station hasreceived a non-voice service request from the network and, if yes,ignoring said non-voice service request, said step of ignoring saidnon-voice service request includes blocking sending of anacknowledgement message generated by the mobile station based on saidnon-voice service request.

The present invention further provides a method of enhancing theprobability of a successful emergency callback to a mobile station in anetwork from an emergency service centre, the method comprising thesteps of: during a callback period, monitoring whether the mobilestation has received a service request from the network and, if yes,ignoring said service request if said service request is a non-voiceservice request that is anything but a position location servicerequest, said step of ignoring said service request includes blockingsending of an acknowledgement message generated by the mobile stationbased on said non-voice service request.

The present invention still further provides a method of enhancing theprobability of a successful emergency callback to a mobile station in anetwork from an emergency service centre, the method comprising the stepof: during a callback period, monitoring whether a user attempts toinitiate a non-voice service request that is anything but a positionlocation service request, and if yes ignoring said non-voice servicerequest.

The present invention yet further provides a mobile station forenhancing the probability of successful emergency call completion to anetwork and successful callback from emergency service centre, themobile station comprising: a communications subsystem, saidcommunications subsystem including a receiver, a transmitter and adigital signal processor; a microprocessor communicating with saiddigital signal processor of said communications subsystem; user inputand output means communicating with said microprocessor; memorycommunicating with said microprocessor; and an emergency service module,said emergency service module communicating with both said digitalsignal processor and said microprocessor, wherein during an emergencycall attempt or callback said emergency service module directs saidmicroprocessor to ignore non-voice service requests other than positionlocation service requests from said network, the ignoring of thenon-voice service requests including blocking sending of anacknowledgement message generated by the mobile station based on saidnon-voice service request.

Other aspects and features of the present application will becomeapparent to those ordinarily skilled in the art upon review of thefollowing description of specific embodiments of a method and apparatusfor a mobile station to enhance the probability of successful emergencycall completion and successful callback from emergency service centre inconjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the attached figures, wherein:

FIG. 1 is a block diagram illustrating an example CDMA network;

FIG. 2 is a flow chart of an emergency call attempt according to themethod of the present invention;

FIG. 3 is a flow chart of device initiated calls during emergencycallback mode according to the method of the present invention;

FIG. 4 is a flow chart of network initiated calls during emergencycallback mode according to the method of the present invention;

FIG. 5 is a block diagram illustrating a mobile station that can beconfigured to both act as the MS of FIG. 1 and include preferredembodiments of the apparatus and method of the current application.

Same reference numerals are used in different figures to denote similarelements.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to the drawings, FIG. 1 is a block diagram illustrating anexample CDMA network 100. The following blocks are shown in FIG. 1:

-   -   MS 20: Mobile Station;    -   PDE: Position Determination Entity;    -   MPC: Mobile Position Centre;    -   CRDB: Coordinate Routing Database;    -   ESNE: Emergency Services Network Entity;    -   ESME: Emergency Services Message Entity; and    -   PSAP 120: Public Safety Answering Point.

The above blocks are known to those skilled in the art and with theexception of the mobile station will not be outlined in detail below.

When the user places an emergency call, the MS ignores anynetwork-initiated mobile-terminated non-voice services. Any page fromthe network to establish such services is ignored for the duration ofongoing emergency call set-up attempts unless and until the usermanually terminates emergency call attempts. Examples of non-voiceservices include Data, Short Message Service (SMS), Over-The-AirParameter Administration (OTAPA) etc. This enhances the probability ofsuccessful emergency call origination since the MS ensures thatemergency call origination process is not disrupted by network-initiatednon-voice services.

When the MS is in emergency callback mode, it prevents the user frominitiating any non-voice services except position location services. Inaddition, the MS refrains from making any autonomous user-invisibleMS-initiated non-voice services. One example of such services isinitiation of an autonomous data session for a variety of reasons suchas reconnection or maintenance of data connectivity on an “always onalways connected” data-capable MS. Stopping these services from beingoriginated from the MS enhances the probability that the emergency callcentre can successfully call the user during callback period. This isquite important when the MS has locked onto a less preferred wirelesssystem. Any non-emergency call attempts in such condition will force theMS to exit the system and thereby making the MS unreachable from theemergency call centre.

When the MS is in emergency callback mode, the mobile station ignoresany network-initiated non-voice services except network-initiatedposition location services. Ignoring these network-initiated servicesfrom being established during this period enhances the probability thatthe emergency call centre can successfully call the user during callbackperiod.

If there is a page match (or any equivalent mechanism indicating thatthe network wants to communicate with the MS) and the proposed serviceoption indicates one of the above mentioned services during callbackperiod, MS simply fakes that it did not receive the page or indicationfrom the network and does not send any response back to the networkduring the Emergency Call attempt period and the Emergency Call BackMode period. With this mechanism, without any assistance from thenetwork, the mobile device makes certain that any emergency call attemptor any mobile terminated call from the Emergency Services will beuninterrupted by any non voice call attempts. Other means of non voicecall ignore could have been undertaken such as non voice call rejectmessage to the network but that would require additional changes in thenetwork side to handle such scenario.

If the MS receives any form of acknowledgement from the network inresponse to its emergency call attempt but the traffic channel set-upfails due to fading or any other reasons, the MS still enters callbackmode and provides visual callback display to the user. In such case,emergency callback centre can still retrieve the mobile's callbacknumber from its origination attempt and place a call to the MS.

If the mobile is already in some form of communication with the networksuch as in autonomous data session to maintain connectivity or in overthe air service provisioning etc., an attempt by the user to make anemergency call will immediately end any previous session and theemergency call session will proceed. As the previous call session hasjust ended, the mobile device will try to acquire this system for theemergency call. Under the circumstances of mobile device failing toacquire this system, the device will try to acquire other systems, i.e.,channels, which the mobile is allowed to acquire. In order to increasethe probability of system acquisition, within the scan of other allowedsystems, the mobile device will try to acquire the first system every 3seconds or for a time period similar to that order. In this way, theprobability of successful emergency call will be increased under thecircumstances when an ongoing session with the network has beeninterrupted in order to provide a user a service for emergency callattempt. If the mobile device fails to acquire any system that it isallowed to acquire (regardless of whether it is preferred or not), itwill attempt to acquire any other system on the frequency bandssupported by it.

Reference is now made to FIG. 2 regarding one way of implementing theabove as illustrated. A user places an emergency call in step 40 and themobile station 20 moves to step 42. In step 42, the mobile station 20checks whether the device is already communicating with the network. Ifso, the mobile station moves to step 44 in which the communication withthe network is terminated and to step 46 in which mobile device 20 triesto reacquire a system for the emergency call.

If in step 42 the device is not communicating with the network, or ifthe device is communicating and moves through steps 44 and 46, themobile system next moves to step 48. In step 48 the mobile device sendsan emergency call request to the network and it further ignores anynon-voice pages from the network until a regular mode is entered.

Mobile station 20 next moves to step 50 in which it checks whether thenetwork call request was successful. If yes, mobile station 20 moves tostep 52 in which an emergency call is placed and once the emergency callis finished, the mobile station 20 moves to step 54 in which the call isended. Mobile station 20 next moves to step 56 in which emergencycallback mode is entered.

As one skilled in the art will appreciate, the emergency callback modeallows the device to be contacted by the emergency services networkentity and ensure that the call will be uninterrupted by any non-voicecall attempts.

If in step 50 the emergency call request to the network wasunsuccessful, the system next moves to step 60. In step 60 the mobilestation 20 checks whether the reason that the call was unsuccessful wasbecause the user aborted the call. If the user aborted the call, themobile station moves to step 62 in which the mobile station 20 movesinto a regular mode.

Conversely, if the user did not abort in step 60, this mobile station 20moves to step 64 in which it continues to try to acquire a new system asrequired and, based on this, further moves back to step 48.

Thus the mobile station will continue to attempt to acquire a networkfor the emergency call until either it has successfully completed theemergency call and ended in which case it will move into an emergencycallback mode or, in the case of the user aborting the emergency callattempt, in which case the mobile station 20 enters a regular mode.

Reference is now made to FIG. 3. Once the mobile station 20 moves intoan emergency callback mode 70, a user may attempt to initiate callsduring this callback mode. In step 72 the mobile device requests aservice and the mobile station 20 moves to step 74. In step 74 themobile station 20 checks whether the service is an emergency call. If itis an emergency call, the mobile station 20 moves to step 76 in whichthe call is started and once the call is completed, the mobile station20 moves to step 78. Because a new emergency call has been placed, thecallback timer needs to be restarted, and this is accomplished in step80.

Once the emergency callback timer is reset, then the system moves backinto waiting in an emergency callback mode in step 70.

If the service request in step 74 is found to be a non-emergency call,the system moves to step 82. In step 82 the mobile station determineswhether the service request is a non-emergency voice request or aposition location request. If it is a non-emergency voice or a positionlocation request, the mobile station 20 moves to step 84 in which itchecks whether the service is allowed on the current system. If themobile station 20 finds in step 84 that the service is allowed on thecurrent system, then the mobile device next moves to step 85 in which itchecks whether the service is a non-emergency voice service.

If in step 85 the mobile station finds that the service is anon-emergency voice service, then the call is started in step 86 andonce it is over it is ended in step 88 and then moves into step 90 inwhich the regular mode is entered.

If in step 85 the mobile station finds that the service is not annon-emergency voice service the call is started in step 87 and once itis over is ended in step 89 and the mobile station next moves to step 98in which checks whether the callback timer has expired.

If in step 84 the mobile station 20 determines that the service is notallowed on the current system then the mobile station 20 moves to step92 in which it checks whether the user accepts exiting the callback modeon the current system. If in step 92 the user does accept exiting thecallback mode, the mobile station moves to step 94 in which a new systemis acquired that supports this call request and then back to step 86 inwhich the call is started, step 88 in which the call is ended, and step90 in which the regular mode is entered.

If in step 92 the user does not accept exiting the callback mode or ifin step 82 it is determined that the service request is not a positionlocation request or a non-emergency voice request then the mobilestation moves to step 96. In step 96 the mobile station 20 ignores therequest and then moves to step 98 in which it checks whether thecallback timer has expired.

If the callback timer has expired in step 98, the mobile device movesinto regular mode 90. Otherwise, it moves back to step 70 in which itwaits in an emergency callback mode.

Therefore, based on the above, when a user attempts to place a callduring the emergency callback mode, the mobile device checks whether itis an emergency call, in which case the call is placed, or anon-emergency voice call or a position location call and whether that isallowed on the current system and, if it is, then the call is placed andthe mobile station 20 moves into a regular mode. Otherwise, the mobiledevice waits until the callback timer is expired before it moves intoregular mode.

Reference is made to FIG. 4. In FIG. 4, the mobile station 20 is inemergency callback mode 70. In step 100, mobile station 20 receivesindication that network wants to initiate a call. The mobile station 20moves to step 102. In step 102 the mobile station 20 checks whether thenetwork initiated call request is a non-voice service request or a voiceservice request. If it is a non-voice service request, the mobilestation moves to step 104 in which it checks whether the request is aposition location service.

If in step 102 the call is found to be a voice service request or if instep 104 the call is found to be a position location service, the mobilestation 20 next moves to step 106. In step 106 the call is set up andwhen finished the mobile station moves to step 108 in which the call isended.

Mobile station 20 next moves to step 110 in which it checks whether thecallback timer has expired. If the callback timer has expired, mobilestation 20 moves to step 112 in which the emergency callback mode isended and the regular mode is entered into.

Conversely, if the callback timer has not yet expired, the system movesto step 70 and stays in emergency callback.

If in step 104 it is found that the non-voice service request is not aposition location service the system moves to step 114 in which theservice request is ignored, and mobile station 20 next moves back tostep 110 in which it checks whether the callback timer is expired.

Turning now to FIG. 5, FIG. 5 is a block diagram illustrating a mobilestation that can be configured to both act as the MS of FIG. 1 andinclude preferred embodiments of the apparatus and method of the currentapplication. Mobile station 200 is preferably a two-way wirelesscommunication device having at least voice and data communicationcapabilities. Mobile station 200 preferably has the capability tocommunicate with other computer systems on the Internet. Depending onthe exact functionality provided, the wireless device may be referred toas a data messaging device, a two-way pager, a wireless e-mail device, acellular telephone with data messaging capabilities, a wireless Internetappliance, or a data communication device, as examples.

Where mobile station 200 is enabled for two-way communication, it willincorporate a communication subsystem 211, including both a receiver 212and a transmitter 214, as well as associated components such as one ormore, preferably embedded or internal, antenna elements 216 and 218,local oscillators (LOs) 213, and a processing module such as a digitalsignal processor (DSP) 220. As will be apparent to those skilled in thefield of communications, the particular design of the communicationsubsystem 211 will be dependent upon the communication network in whichthe device is intended to operate. For example, mobile station 200 mayinclude a communication subsystem 211 designed to operate within theMobitex™ mobile communication system, the DataTAC™ mobile communicationsystem, GPRS network, UMTS network, EDGE network or CDMA network.

Network access requirements will also vary depending upon the type ofnetwork 219. For example, in the Mobitex and DataTAC networks, mobilestation 200 is registered on the network using a unique identificationnumber associated with each mobile station. In UMTS and GPRS networks,and in some CDMA networks, however, network access is associated with asubscriber or user of mobile station 200. A GPRS mobile stationtherefore requires a subscriber identity module (SIM) card in order tooperate on a GPRS network, and a RUIM in order to operate on some CDMAnetworks. Without a valid SIM/RUIM card, a GPRS/UMTS/CDMA mobile stationmay not be fully functional. Local or non-network communicationfunctions, as well as legally required functions (if any) such as “911”emergency calling, may be available, but mobile station 200 will beunable to carry out any other functions involving communications overthe network 200. The SIM/RUIM interface 244 is normally similar to acard-slot into which a SIM/RUIM card can be inserted and ejected like adiskette or PCMCIA card. The SIM/RUIM card can have approximately 64K ofmemory and hold many key configuration 251, and other information 253such as identification, and subscriber related information.

When required network registration or activation procedures have beencompleted, mobile station 200 may send and receive communication signalsover the network 219. Signals received by antenna 216 throughcommunication network 219 are input to receiver 212, which may performsuch common receiver functions as signal amplification, frequency downconversion, filtering, channel selection and the like, and in theexample system shown in FIG. 5, analog to digital (A/D) conversion. A/Dconversion of a received signal allows more complex communicationfunctions such as demodulation and decoding to be performed in the DSP220. In a similar manner, signals to be transmitted are processed,including modulation and encoding for example, by DSP 220 and input totransmitter 214 for digital to analog conversion, frequency upconversion, filtering, amplification and transmission over thecommunication network 219 via antenna 218. DSP 220 not only processescommunication signals, but also provides for receiver and transmittercontrol. For example, the gains applied to communication signals inreceiver 212 and transmitter 214 may be adaptively controlled throughautomatic gain control algorithms implemented in DSP 220.

Mobile station 200 preferably includes a microprocessor 238 whichcontrols the overall operation of the device. Communication functions,including at least data and voice communications, are performed throughcommunication subsystem 211. Microprocessor 238 also interacts withfurther device subsystems such as the display 222, flash memory 224,random access memory (RAM) 226, auxiliary input/output (I/O) subsystems228, serial port 230, keyboard 232, speaker 234, microphone 236, ashort-range communications subsystem 240 and any other device subsystemsgenerally designated as 242.

Some of the subsystems shown in FIG. 5 perform communication-relatedfunctions, whereas other subsystems may provide “resident” or on-devicefunctions. Notably, some subsystems, such as keyboard 232 and display222, for example, may be used for both communication-related functions,such as entering a text message for transmission over a communicationnetwork, and device-resident functions such as a calculator or tasklist.

Operating system software used by the microprocessor 238 is preferablystored in a persistent store such as flash memory 224, which may insteadbe a read-only memory (ROM) or similar storage element (not shown).Those skilled in the art will appreciate that the operating system,specific device applications, or parts thereof, may be temporarilyloaded into a volatile memory such as RAM 226. Received communicationsignals may also be stored in RAM 226.

As shown, flash memory 224 can be segregated into different areas forboth computer programs 258 and program data storage 250, 252, 254 and256. These different storage types indicate that each program canallocate a portion of flash memory 224 for their own data storagerequirements. Microprocessor 238, in addition to its operating systemfunctions, preferably enables execution of software applications on themobile station. A predetermined set of applications that control basicoperations, including at least data and voice communication applicationsfor example, will normally be installed on mobile station 200 duringmanufacturing. A preferred software application may be a personalinformation manager (PIM) application having the ability to organize andmanage data items relating to the user of the mobile station such as,but not limited to, e-mail, calendar events, voice mails, appointments,and task items. Naturally, one or more memory stores would be availableon the mobile station to facilitate storage of PIM data items. Such PIMapplication would preferably have the ability to send and receive dataitems, via the wireless network 219. In a preferred embodiment, the PIMdata items are seamlessly integrated, synchronized and updated, via thewireless network 219, with the mobile station user's corresponding dataitems stored or associated with a host computer system. Furtherapplications may also be loaded onto the mobile station 200 through thenetwork 219, an auxiliary I/O subsystem 228, serial port 230,short-range communications subsystem 240 or any other suitable subsystem242, and installed by a user in the RAM 226 or preferably a non-volatilestore (not shown) for execution by the microprocessor 238. Suchflexibility in application installation increases the functionality ofthe device and may provide enhanced on-device functions,communication-related functions, or both. For example, securecommunication applications may enable electronic commerce functions andother such financial transactions to be performed using the mobilestation 200.

In a data communication mode, a received signal such as a text messageor web page download will be processed by the communication subsystem211 and input to the microprocessor 238, which preferably furtherprocesses the received signal for output to the display 222, oralternatively to an auxiliary I/O device 228. A user of mobile station200 may also compose data items such as email messages for example,using the keyboard 232, which is preferably a complete alphanumerickeyboard or telephone-type keypad, in conjunction with the display 222and possibly an auxiliary I/O device 228. Such composed items may thenbe transmitted over a communication network through the communicationsubsystem 211.

For voice communications, overall operation of mobile station 200 issimilar, except that received signals would preferably be output to aspeaker 234 and signals for transmission would be generated by amicrophone 236. Alternative voice or audio I/O subsystems, such as avoice message recording subsystem, may also be implemented on mobilestation 200. Although voice or audio signal output is preferablyaccomplished primarily through the speaker 234, display 222 may also beused to provide an indication of the identity of a calling party, theduration of a voice call, or other voice call related information forexample.

Serial port 230 in FIG. 5, would normally be implemented in a personaldigital assistant (PDA)-type mobile station for which synchronizationwith a user's desktop computer (not shown) may be desirable, but is anoptional device component. Such a port 230 would enable a user to setpreferences through an external device or software application and wouldextend the capabilities of mobile station 200 by providing forinformation or software downloads to mobile station 200 other thanthrough a wireless communication network. The alternate download pathmay for example be used to load an encryption key onto the devicethrough a direct and thus reliable and trusted connection to therebyenable secure device communication.

Other communications subsystems 240, such as a short-rangecommunications subsystem, is a further optional component which mayprovide for communication between mobile station 200 and differentsystems or devices, which need not necessarily be similar devices. Forexample, the subsystem 240 may include an infrared device and associatedcircuits and components or a Bluetooth™ communication module to providefor communication with similarly enabled systems and devices.

When mobile device 200 is used as the MS 20 of FIG. 1, emergency servicemodule 246 and transceiver 211 cooperate with a method and apparatus fora mobile station to enhance the probability of successful emergency callcompletion and successful callback from emergency service centre. Theemergency service module 246 is shown connected to both microprocessor238 and DSP 220 of transceiver 211, so that the higher layer concernscan be handled by the microprocessor 238 whereas the lower layersconcerns can be handled by the DSP 220.

The above-described embodiments of the present application are intendedto be examples only. Those of skill in the art may effect alterations,modifications and variations to the particular embodiments withoutdeparting from the scope of the application.

1. A method of enhancing the probability of a successful emergency callcompletion on a mobile station in a network, comprising the steps of:during an emergency call attempt by a mobile station, monitoring whetherthe mobile station has received a non-voice service request from thenetwork and, if yes, ignoring said non-voice service request, said stepof ignoring said non-voice service request includes blocking sending ofan acknowledgement message generated by the mobile station based on saidnon-voice service request.
 2. The method of claim 1, further comprisingthe steps of: at the start of an emergency call attempt, checkingwhether the mobile station is already communicating with the network,and if yes, ending the communication with the network.
 3. The method ofclaim 2, further comprising the steps of: if said communication with thenetwork is ended, attempting to acquire a network for the emergency callattempt.
 4. The method of claim 3, wherein said step of attempting toacquire a network includes periodically attempting to reacquire saidnetwork that communication was ended with.
 5. The method of claim 1,wherein the mobile station is allowed to acquire any network regardlessof whether the network is preferred.
 6. The method of claim 5, whereinsaid mobile station can acquire a network even if a subscriber identitymodule or a removable user identity module is not present.
 7. The methodof claim 1, further comprising the steps of: sending an emergency callrequest to the network; checking whether the emergency call request wassuccessful; if said emergency call request was unsuccessful, checkingwhether the user aborted the emergency call request; and if said userdid not abort said emergency call request, attempting to acquire a newsystem.
 8. A method of enhancing the probability of a successfulemergency callback to a mobile station in a network from an emergencyservice centre, the method comprising the steps of: during a callbackperiod, monitoring whether the mobile station has received a servicerequest from the network and, if yes, ignoring said service request ifsaid service request is a non-voice service request that is anything buta position location service request, said step of ignoring said servicerequest includes blocking sending of an acknowledgement messagegenerated by the mobile station based on said non-voice service request.9. The method of claim 8, wherein said method further includes the stepsof: setting up a call for a voice service request or a non-voiceposition location service request; ending said call; checking whether acallback timer has expired, and if so entering a regular mode.
 10. Amobile station for enhancing the probability of successful emergencycall completion to a network and successful callback from emergencyservice centre, the mobile station comprising: a communicationssubsystem, said communications subsystem including a receiver, atransmitter and a digital signal processor; a microprocessorcommunicating with said digital signal processor of said communicationssubsystem; user input and output means communicating with saidmicroprocessor; memory communicating with said microprocessor; and anemergency service module, said emergency service module communicatingwith both said digital signal processor and said microprocessor, whereinduring an emergency call attempt or callback said emergency servicemodule directs said microprocessor to ignore non-voice service requestsother than position location service requests from said network, theignoring of the non-voice service requests including blocking sending ofan acknowledgement message generated by the mobile station based on saidnon-voice service request.
 11. The mobile station of claim 10, whereinsaid emergency service module further directs said microprocessor todrop existing network communications during said emergency call attempt.12. The mobile station of claim 11, wherein said emergency servicemodule further directs said microprocessor to block any user initiated,non-position location service requests from a user during a callbackperiod.
 13. The mobile station of claim 10, further comprising asubscriber identity module/removable user identity module interface. 14.The mobile station of claim 13, wherein said mobile station can acquirea network during an emergency call attempt without a subscriber identitymodule or a removable user identity module present in said subscriberidentity module/removable user identity module interface.